This invention relates to a magnet wire having high lubricity.
A recent trend in the manufacture of electric devices using enameled wires is to achieve faster production by using a high-speed auto-winder. However, the insulation layer of an enameled wire tends to be mechanically damaged during winding due to friction, and after the wire is built into an electric device, layer-shorting may occur causing a great increase in the loss factor. To reduce such mechanical damage, an enameled wire having good lubricity has been desired. Good lubricity is also needed for manual insertion of an enameled wire into a small slot in a motor. Since the enameled wire itself has poor lubricity, the stated object has been achieved by coating the enameled wire with liquid lubricants such as liquid paraffin and refrigerating machine oil. On the other hand, the need for an enabeled wire having high mechanical strength and scrape resistance sufficient to avoid mechanical damage during winding has been partially met by using a nylon overcoated enameled wire or polyamideimide overcoated enameled wire.
Nowadays, there is a need for motors and transformers of even higher efficiency to achieve energy conservation, and the need is particularly great with motors, such as hermetic motors used in air conditioners and refrigerators. To meet this end, even more enameled wires are inserted into a small slot in a motor to achieve a higher space factor. Conventionally, most hermetic motors have used certain polyester imide or polyamideimide overcoated enameled wires that are high not only in mechanical strength and scrape resistance, but also in refrigerant resistance. In addition, to prevent deterioration due to winding or to realize efficient coil insertion into a slot, these enameled wires have been coated with refrigerating machine oil in most cases. However, when an attempt is made to increase the efficiency of a motor by inserting more enameled wires into a small slot so as to achieve a higher space factor, many problems arise that can hardly be solved by the conventional enameled wires coated with refrigerating machine oil or other known lubricants.
First, liquid lubricants such as refrigerating machine oil do not have an adequate lubricating property and slipperiness, so a desired large number of enameled wires cannot be accommodated in the slot, and should they be forcibly inserted by applying greater force, the coating of insulation can be mechanically damaged, thus increasing the possibility of layer-shorting. Second, due to poor lubricity, enameled wire in the motor will be subjected to electromagnetic vibrations that can also cause mechanical damage to the insulation coating, whereupon layer-shorting may occur and the motor will fail to perform its function.
An attempt to provide improved lubricity by applying a great volume of liquid lubricant has little effectiveness, and worse than that, it increases the tendency of dust to be deposited on the enameled wire. Furthermore, excessive oil can adversely affect the bonding power of an adhesive tape used for sealing the coil ends. Coating the enameled wire with solid paraffin, carnauba wax and other solid lubricants that have better lubricating property and slipperiness than liquid lubricants has been tried, but when the enameled wire coated with such solid lubricants is applied to a hermetic motor, a lubricant extracted with the refrigerant can clog the opening of the compressor valve or the refrigerant expansion valve in the refrigerator, thereby reducing the refrigerating capacity of the machine. The extracted lubricant also reduces the lubricity and slipperiness of the enameled wire and makes the insulating coating more vulnerable to damages caused by electromagnetic vibrations. The solid lubricants are usually applied to the enameled wire as a solution wherein a few percent of the lubricant is dissolved in solvents such as petroleum benzine and xylene. However, the use of large amounts of low-boiling solvents is not only hazardous and toxic, but also causes crazing in some types of electric wires, thus destroying their commercial value. Therefore, solid lubricants can only be applied to limited types of wire.
Another method proposed for providing an enameled wire with good lubricating properties is to coat a conductor with an insulating wire enamel that contains synthetic resins having high lubricating property such as polyethylene, polypropylene and ethylene tetrafluoride resin, as well as liquid or solid lubricants such as silicone oil, fluorine-containing surfactants, paraffin wax, carnauba wax and montan wax. But since synthetic resins such as polyethylene, polypropylene and ethylene tetrafluoride resin are only sparingly soluble in solvents typically used for the insulating wire enamel, it is not easy to disperse them in the wire enamel uniformly, and the resulting wire enamel has low stability. What is more, these resins are not miscible with the enamel insulating material; hence, it is not easy to provide an insulating coating having good appearance in which the resins are uniformly dispersed.
Liquid lubricants mixed with the insulating wire enamel do not provide any better slipperiness and lubricating property than when they are directly applied to the enameled wire.
Solid lubricants in the insulating wire enamel may be extracted with the refrigerant or solvent, as in the case when they are directly applied to the enameled wire, and so a method of using an insulating wire enamel that contains solid lubricants is not easy to apply to the manufacture of an enameled wire for hermetic motors. In addition, like the synthetic resins, solid lubricants are sparingly soluble in solvents for the insulating wire enamel, and are not miscible with the enamel insulating material. Thus, the resulting wire enamel is not stable, and it is difficult to provide an insulating coating of good appearance in which the solid lubricants are uniformily dispersed.